p and u chart formats | p chart format options

p and u chart formats
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p charts and u charts can have upper control limits (UCL) and lower control limits (LCL) that vary with the sample size. The QI Macros provides users with options about how these control limits are displayed.

Flat or skyline limits without 1 and 2 sigma lines (default)
How to choose between flat/skyline limits and wavy limits
Wavy limits with 1 and 2 sigma lines
Show/Don't Show 1 and 2 sigma lines
Wavy limits without 1 and 2 sigma lines

If there is very little variation in your sample size, the p chart and u chart will have horizontal control lines.

Flat horizontal lines when there is little variation in the sample size

Since the p chart is a fraction defective chart, the UCL is limited to 100% and the LCL is limited to 0%.

p chart example of UCL Limited to 100%

Flat or skyline limits without 1 and 2 sigma lines (default)

Here is a p chart using the QI Macros defaults

p chart with flat control limits

How to choose between flat (skyline) and wavy limits

The QI Macros defaults to the flat/skyline limits. To change to the wavy limits, click on Control Charts, then Control Chart Rules, then p/u UCL_LCL format.

change p chart control limit format

A window will open showing the new format you are selecting. Click OK to change the format.

p chart control limit prompt

Wavy limits with 1 and 2 sigma lines

The new format will be wavy limits with 1 and 2 sigma lines.

p chart with wavy control limits and sigma lines

Show/Don't Show the 1 and 2 sigma lines

To hide the 1 and 2 sigma lines, click on Control Charts, then Control Chart Rules, then Show/Don't Show 1 and 2 sigma lines.

p chart sigma line prompt

Wavy limits without 1 and 2 sigma lines

Here is a p chart without the 1 and 2 sigma lines.

Flat horizontal lines when there is little variation in the sample size

If there is little variation in the sample size, the p chart and u charts will have horizontal control limits. Here is the formula:

p chart example with UCL limited to 100%

Since the p chart is a fraction defective chart, the UCL is limited to 100% and the LCL is limited to 0%

p chart with UCL ceiling of 100%

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If you already own the QI Macros, you can purchase an upgrade. You must purchase one upgrade for each license you own.

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